[gtkmm] Ruler position indicator

[Gregory P Bayard Dartmouth EDU (Gregory P. Bayard)]

I am unable to connect the ruler position indicator to
motion events in a Gtk::DrawingArea.  There is a large
amount of example source code on the internet that no longer
compiles with gtkmm-2.0.  The code on the net shows,

drawing_area.motion_notify_event.connect(horiz_ruler.motion_notify_event.slot());

Neither the Gtk::DrawingArea nor the Gtk::HRuler have a
motion_notify_event.  The new versions of the objects have
signal_motion_notify_event() and on_motion_notify_event()
methods.  Intuitively I figured the following would work,

drawing_area.signal_motion_notify_event.connect(horiz_ruler.on_motion_notify_event.slot());

Sadly, it does not work, as on_motion_notify_event does not
provide a slot().  Does anyone have any idea how to move the
indicator with the mouse on a ruler in gtkmm-2.0?

Thanks,
Gregory Bayard